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Charging Lumia 920 without wires

Nokia Lumia 920 with wireless charger

There’s a lot to be said for getting wires out of the way of digital devices – for one thing it makes them mobile. A smartphone wouldn’t be much use if you needed to jack it in every time you make a call or check Facebook. And let’s not forget Mobile networks, Wi-Fi and Bluetooth all cut down the need for cable spaghetti.

Despite all this, you still need to connect a phone to a wall socket to give them juice. At least you did. That’s about to change with wireless charging.

Nokia is the first phone maker to deliver a smartphone that can recharge its batteries without being plugged in. In fact, there’s no longer any need to physically connect a cable to the Lumia 920.

This is done by magnetic induction. Induction tops up your phone battery when the charging pad converts current into an alternating electromagnetic field. The phone then converts this back to a current to charge the battery. If that sounds too complex, just remember it’s the same as the charging technology used by wireless toothbrushes.

Hot stuff

Nokia’s wireless charging is about 90% as efficient as using a wire charger and some of the lost energy converts to heat – this means the phone can get warm during charging. In testing I found the phone was noticeably warm, but not alarmingly hot. Certainly nothing like enough to burn.

It’s a simple enough business – although as we will see there are traps for young players.

Nokia’s DT-900 charging plate is a little smaller than the Lumia 920. It comes with a weirdly wide electrical plug – if you use a multi-socket or a distribution board it has to sit in the left-most outlet. This connects to the plate. You simply sit your phone on the plate to start charging. A white LED lights on the plate and the phone bleeps to let you know everything is working.

What could possibly go wrong? Well, for the first day I had the device I thought it wasn’t working because I was using the plate upside down. The orientation isn’t immediately obvious – in fact, counterintuitively, the bottom face is slightly smaller than the top.

Simple

With that confusion behind me it was all plain sailing. Or should that be plain charging? I found it takes slightly longer to charge using the plate than a direct cable – but only a few minutes. The phone can go from almost discharged to a full charge in under two hours.

Nokia’s documentation says you can leave the pad switched on when you’re not charging as it draws hardly any power when not in use. If that bothers you, then it’s not hard to flick the wall switch.

Easy, not entirely wire free

Not entirely wire free

To be blunt, placing the phone on the mat isn’t that much less effort than plugging in a cable. And let’s face it, the charging plate has wires, so you’re not entirely wire free. But there’s no need to worry about having the right cable – I’ve six incompatible USB connectors sitting my desk drawer, finding the right one in a hurry can be stressful.

The good news is that Nokia’s charging plate uses the Qi standard. That means it’ll work with other devices. It’s still early days for Qi, other phone makers are preparing to launch Qi models and over time you’ll see tablets and other gizmos built around the same standard. Even better news is there are plans to install Qi charging mats in public places – so you’ll be able to charge while on the move. There’s no news on when or if these public chargers will reach New Zealand.

My iPhone gets hot anyway when I charge it, attenuation and resistance happens any time you apply current through a circuit. If there is no termination then it doesn’t go anywhere, but otherwise it must flow to a receiver. This is the same technology now seen overseas for charging EV’s isn’t it? Now if only I could get interest free finance and feed in tariffs that make sense, I.e. support to provide power back into the grid, I’ll just use solar power. After all we are invested in sustainability in New Zealand right?

Efficiency isn’t that bad. Nokia claims 90%. I noticed it takes about 100 minutes to fully charge compared to around 80 minutes when plugged in – of course this may not be directly related to efficiency. There’s a bit of heating, enough to keep your hands warm in cold weather, but certainly not enough to burn.